This paper establishes the model of the hose-drogue aerial refueling system (HDARS) with variable length and dynamics analysis implemented during trailing and coupling. By utilizing the finite segment multi-body dynamics method, the kinematics and dynamics equations of the HDARS are obtained in the process of trailing. Further, considering that the hose whipping phenomenon (HWP) causes tremendous load on the probe, the dynamics of the HDARS in the process of coupling are analyzed. As a result, the explicit formulations of the probe load are derived, which can be applied to directly evaluate both the intensity of the HWP and the effectiveness of the corresponding suppression methods. Moreover, the deployment and retrieval conditions are utilized to achieve the variable length of the HADRS. Several simulations verify the superiority of the proposed model and dynamics analysis method.